226 



PROCEEDINGS OF THE AMERICAN ACADEMY 



ceiver which contains the rods, interferes with the ease of the experi- 

 ment in void spaces. It is necessary, therefore, to be content with 

 the length of arc which can be obtained in common air, and to seek 

 only to regulate as far as possible the consumption of carbon, and the 

 distance at which the extremities of the rods must be held in order 

 that the luminous arc produced shall have its maximum intensity. 

 The first contrivances for attaining this end were not successful. The 

 carbon rods were pushed together by the hand in proportion as they 

 diminished in length ; but they received not the necessary regularity 

 or proportional quantity of motion. Petrie in England and Foucault 

 in France had simultaneously the idea of applying the electrical cur- 

 rent itself to regulate the advance of the carbon points, which were to 

 conduct this same current under the form of a luminous jet. The 

 regulator of the electrical light, by Duboscq, rests upon the same 

 principle as the apparatus of the two physicists just named. In the 



regulator of Duboscq, represented in the 

 wood-cut, an electro-magnet, excited by 

 the action of the electrical current which 

 circulates in the copper thread q of the 

 coil B, inside of which is enclosed an iron 

 coqe, F, placed in the base of the instru- 

 ment, attracts into contact a piece of soft 

 iron, K. To this is attached a bent lever, 

 L, which turns at x upon a horizontal axis, 

 and is pressed up by a spring, s, and rests 

 at against a short lever, having its axis 

 of rotation horizontal. This small lever 

 carries at cZ a steel nib, the object of which 

 is to check the toothed wheel r. This 

 wheel has a fly, and an endless screw, 

 V, to which a movement can be given 

 by a second wheel, r', the pinion of Which 

 <C is in connection with the great toothed 

 wheel p. The latter contains the main- 

 spring for moving the machine. This 

 great toothed wheel has two grooves of 

 different diameters, the use of which will 

 soon be indicated, and upon which run 

 the two chains /i, /i', which, after having 

 passed upon the pulleys j) p, p' p', are 



